1. Technical Field
The present invention relates to a negative-working photosensitive material and a negative-working planographic printing plate precursor including the material. In particular, the invention relates to a negative-working photosensitive material which allows direct drawing by infrared laser light, and a negative-working planographic printing plate precursor including the material.
2. Related Art
Conventionally, a PS plate having a lipophilic photosensitive resin layer provided on a hydrophilic support has been widely used as a planographic printing plate precursor, and a desired printing plate is obtained by a plate-making method which usually involves mask exposure (surface exposure) via a lithographic film and then removal of non-image regions by dissolving. In recent years, digitalization techniques which involve electronic processing, accumulation and output of image information using computers have been spreading. A wide variety of new image output systems compatible with such digitalization techniques have come to be used in practical applications. As a result, there has been demand for computer-to-plate (CTP) techniques of producing a printing plate directly by scanning a highly directional light, such as laser light, according to digitalized image information, without employing a lithographic film. A critical technical issue has been the provision of a planographic printing plate precursor suitable for these techniques.
As a planographic printing plate precursor capable of such scanning exposure to light, a planographic printing plate precursor has been proposed which includes, on a hydrophilic support, a lipophilic photosensitive resin layer (hereinafter also referred to simply as a photosensitive layer) including a photosensitive compound capable of generating active species such as radicals or Bronsted acids by laser exposure, and has already been put on the market. When the planographic printing plate precursor is scanned with laser based on digital information, active species are generated. The action of the active species causes physical or chemical changes at the photosensitive layer, making the photosensitive layer insoluble, and by then developing the photosensitive layer, a negative planographic printing plate is obtained. A specific example thereof is a negative-working planographic printing plate precursor having, on a hydrophilic support, a photopolymerizable photosensitive layer including a photopolymerization initiator excellent in photosensitive speed, an ethylenically unsaturated compound capable of addition polymerization, and a binder polymer soluble in an alkali developer. The planographic printing plate precursor has the advantages of being excellent in productivity, convenient for development processing and having favorable resolution and ink affinity and, therefore, has a desirable printing performance.
In this kind of negative-working planographic printing plate precursor, in order to improve the adhesion between the photosensitive layer and the support, and the development removability of an unexposed portion of a photosensitive layer, an undercoat layer is usually provided between the support and the photosensitive layer (see for example, JP-A No. 2001-272787). However, depending on the state of the support, particularly when a support surface is roughened to improve the printing durability, the development removability of an unexposed portion of a photosensitive layer has been insufficient.